This invention relates to a radio data communication system and method for use in carrying out data communication between a radio client terminal (will be simply called a client terminal hereinafter) and an information server through a radio communication network and a wire communication network, such as a public communication network. This invention also relates to the client terminal used in the radio data communication network.
It is a recent trend that radio communication has become popular and has been carried out by the use of a PHS (Personal Handy-phone System), a PDC (Personal Digital Cellular System), or the like. Moreover, such radio communication also tends to be utilized for data transmission which may transmit electronic mail (E-Mail) and which may access WWW servers. Under the circumstances, the communication environment has been ready for such radio communication by the use of a radio data communication protocol, such as PIAFS (PHS Internet Access Forum Standard) or a wire data communication protocol, such as TCP (Transmission Control Protocol). At any rate, compensation has been given about transmission errors which occur in a radio communication network and about data collision which occur in a wire communication network by the radio data communication protocol and the wire data communication protocol. As a result, data transmission can be certainly guaranteed between client servers.
Heretofore, proposal has been made in Japanese Unexamined Patent Publication (JP-A) No. Hei 8-279890, namely, 279890/1996 about a data communication device which can be used in the radio data communication network. With this data communication device, stable communication can be realized by avoiding failure, retransmission, and interruption of data all of which frequently take place during radio communication.
Thus, the data communication device mentioned above can accomplish data communication through the radio communication network and the wire communication network. Specifically, it is possible for the data communication device to realize effective data communication by changing parameters during the radio communication to optimum parameters which are suitable for the radio communication network. For example, increases have been indicated during the radio communication about various values of timers and about retransmission times of commands. This results in a reduction of communication errors.
Herein, it is to be noted that communication may not always be forcibly established on bad communication conditions, such as strong fading condition, low field intensity, in the radio communication network and a heavy load imposed on a server in the wire communication network. This is because such forcible communication under the bad conditions makes a communication time unexpectedly long and consequently gives rise to an undesirable increase of a communication charge.
It is an object of this invention to provide a radio communication system which is capable of shortening a communication time when the communication environment is bad in a radio communication network.
It is another object of this invention to provide a radio communication system of the type described, which is capable of reducing a communication charge and which is capable of realizing reliable data communication.
It is still another object of this invention to provide a client terminal which can be used in the radio communication system mentioned above.
According to an aspect of this invention, a radio communication method is for use in carrying out data communication between a radio terminal and a server and comprises establishing a path between the radio terminal and the server to carry out the data communication, measuring an amount of information left in the radio terminal at a predetermined time instant during the data communication after the path is established, and determining in the radio terminal whether or not the path is switched to an alternative path connected to an alternative server, with reference to the amount of information left in the radio terminal.
The predetermined time instant may be determined after a predetermined amount of information is transmitted through the path established between the radio terminal and the server or may be determined after failure of the information is detected by the server.
The above-mentioned determining comprises receiving, by the radio terminal, alternative information concerned with the alternative path from the server, calculating a transmission time necessary for transmitting the amount of information left in the radio terminal through the path, calculating, on the basis of the alternative information, an alternative transmission time necessary for a total amount of the information from the beginning, comparing the transmission time with the alternative transmission time to select a shorter one of the transmission time and the alternative transmission time, and deciding either one of the path and the alternative path that corresponds to the shorter one of the transmission time and the alternative transmission time.
According to another aspect of this invention, a radio data communication system is for use in carrying out data communication between a radio terminal and a server. The radio terminal comprises establishing means for establishing a path between the radio terminal and the server to carry out the data communication, measuring means for measuring an amount of information left in the radio terminal at a predetermined time instant during the data communication after the path is established, and determining means for determining whether or not the path is switched to an alternative path connected to an alternative server, with reference to the amount of information left in the radio terminal. The determining means may comprise means for receiving alternative information concerned with the alternative path from the server, means for calculating a selected one of a transmission time and a communication charge which are necessary for transmitting the amount of information left in the radio terminal through the path, means for calculating, on the basis of the alternative information, a selected one of an alternative transmission time and alternative communication charge which are necessary for a total amount of the information from the beginning, and means for comparing the selected one of the transmission time and the communication charge with the selected one of the alternative transmission time and the alternative communication charge to select either one of the path and the alternative path.